1. Field of the Invention
The invention relates generally to magnetic bearings and, in particular aspects, to the design of such bearings for resistance to magnetic coil failures.
2. Description of the Related Art
Bearings have a rotatable rotor and a stationary stator within which the rotor rotates. Some means of reducing friction between the rotor and stator is necessary. Magnetic bearings replace ball bearings or lubricants with a magnetic field that maintains the rotor in a spaced relation from the stator and allows the rotor to rotate in an essentially frictionless manner with respect to the stator. Magnetic bearings promise significant improvements for uses in space as, for example, storage of power in flywheels and the like. Magnetic suspensions (MS) satisfy the long life and low loss conditions demanded by satellite and ISS (International Space Station) based flywheels used for Attitude Control and Energy Storage (ACES) service.
Homopolar magnetic bearings are those in which the rotor is exposed to a single magnetic polarity (i.e., north or south). Homopolar magnetic bearings are advantageous since they commonly use permanent magnets for bias flux to increase the actuator's efficiency and reduce heat generation. Points on the surface of the spinning journal in the homopolar bearing do not experience north-south flux reversals thereby reducing rotor losses due to hysteresis and eddy currents. Radial magnetic bearings are bearings in which the rotor is magnetically supported radially with respect to the stator, while “combo” bearings provide magnetic support for the rotor in both the radial and axial directions with respect to the stator.
To create the magnetic field, one or more magnetic coils are disposed within the stator. Often, multiple magnetic coils are placed in the stator to form the magnetic field, as this provides for redundancy. Even with multiple coil stators, however, faults are a problem, and it would be desirable to have a bearing that is fault-tolerant. If one or more of the coils were to fail, the flux coupling that retains the rotor in its spaced relation from the stator may become unstable, allowing contact between the rotor and stator or by a “catcher bearing.”
There are currently no acceptable known techniques for making a homopolar magnetic bearing “fault-tolerant.” The present invention addresses the problems of the prior art.